Mechanical properties of Inconel 718 additively manufactured by laser powder bed fusion after industrial high-temperature heat treatment

Heat treatment of laser powder bed fused (LPBF-ed) Inconel 718 is crucial to achieve desired mechanical properties. Residual stresses, microsegregation, anisotropy, undesirable phases, layered structure, and poor surface quality are the challenges to be faced before LPBF-ed Inconel 718 parts can be industrially implemented. Although heat treatment of Inconel 718 after the LPBF process is widely discussed in the literature, an industrial approach has been neglected, or the proposed heat treatment processes do not address all the aforementioned challenges. Recently, extensive work has been done in the field of high-temperature heat treatment of this material, showing promise. Following current trends, a 4-stage high-temperature heat treatment, developed by considering the industrial approach, is proposed and evaluated in this paper. A structured, microstructural, and mechanical evaluation of the achieved material properties is presented. Several factors were taken into account, including testing orientation in relation to the build direction (0 degrees, 45 degrees, 90 degrees), surface condition (abrasive blasted, machined), testing temperature (21 degrees C, 425 degrees C), specimen size (dia. 4.06 mm, dia. 6.35 mm), application of the HIP process (with, without). After eliminating the influence of surface, subsurface and internal defects, the material is characterized with isotropic properties, regardless of testing orientation in relation to the build direction. Isotropic properties are confirmed for both room temperature and elevated temperatures (425 degrees C). The obtained elongation is >1.5x higher than the literature reports for heat treated LPBF-ed Inconel 718, while maintaining high tensile strength at the average level found in the literature.